The invention of the present application is concerned with polishing compositions, and particularly relates to such compositions, suitable for the polishing of semi-conductive materials, e.g. silicon and germanium, which contain as a polishing agent a novel cmpound of calcium, titanium, zirconium and oxygen hereinafter described.
Slices or wafers cut from single-crystal ingots of semi-conductors such as silicon and germanium are widely used in the manufacture of transistors and similar solid state devices. It is important in such use that the semiconductor surface have a mirror finish and be plane and free from scratches, pits and other defects. Consequently, after the wafers are cut from the boules or ingots, they are polished, with or without preliminary grinding, etching, or lapping. Not only is polishing necessary to obtain the desired surface, but it is also required to make the opposite, flat surfaces of the wafers parallel.
Preliminary grinding or lapping of the wafers, when employed, is usually carried out with an abrasive slurry containing fine alumina, silicon carbide, or diamond abrasive. Hitherto, the polishing compositions most generally used have comprised aqueous slurries of polishing agents such as cerium oxide, ferric oxide, zirconium dioxide, and silicon dioxide, The slurry is applied to the surface of the semi-conductor wafers and a cloth polishing pad is employed. Obviously, the particle size of the polishing agents employed must be controlled and all particles large enough to produce scratches must be eliminated. The effectiveness of a polishing composition is determined both by the perfection of the surface characteristics resulting from its use and by the polishing time required to obtain a desired or acceptable finish.
The polishing time required with a polishing composition depends largely upon (a) the physical characteristics of the polishing agent, particularly its hardness and particle size; (b) the concentration of the polishing agent in the composition; and (c) the presence of absence of certain other ingredients in the composition. In general, the polishing rate, i.e. the rate at which the scratches are removed and a mirror-like surface is obtained, is higher with harder polishing agents, with increased particle size thereof, and with higher concentrations of polishing agent in the slurry. However, increased hardness of the polishing agent and large particles thereof are likely to present problems with scratching of the surface and increasing the concentration of the agent in the composition may reduce the viscosity of the latter sufficiently to cause difficulty in feeding it evenly. As a result, other ingredients are often added to the compositions to increase the polishing rate.
As an example, it is disclosed in U.S. Pat. No. 3,429,080, granted Feb. 25, 1969, that oxidizing compounds such as hydrogen peroxide, sodium peroxide, potassium permanganate, and sodium hypochlorite, when incorporated in small amount in polishing compositions, materially increase the polishing rate of certain polishing agents.